that is all popsts are reviewed by the Moderator of that board before they post.  Sometimes very quick but can take 24 hours I believe.  It's near impossible to reply in a thread as the discussion can move ahead before your reply appears.
If you log in frequently, post & participate without causing a problem, your local moderator will "unmoderate" you.  Read the Newbie Manual, read the rules for each board (like ads only on local board, only 1 ad every 7 days).  
Once you learn the ropes, you'll like it here.
skb